Fiber optical beam delivery device producing output exhibiting intensity distribution profile having non-zero ellipticity

ABSTRACT

An optical beam delivery device formed of optical fibers that are configured to produce an output exhibiting an intensity distribution profile having non-zero ellipticity includes a first length of fiber through which an incident optical beam having beam characteristics propagates and which has a first refractive index profile (RIP). The first RIP enables, in response to an applied perturbation, modification of the beam characteristics of the optical beam to form an adjusted beam having modified beam characteristics relative to the beam characteristics of the optical beam. A second length of fiber is coupled to the first length of fiber and formed with a set of one or more confinement regions that define a second RIP and confine at least a portion of the adjusted beam to generate, at an output of the second length of fiber, an intensity distribution profile having non-zero ellipticity.

RELATED APPLICATIONS

This application is a continuation-in-part of each of the followingapplications filed May 26, 2017: U.S. patent application Ser. Nos.15/607,399; Ser. No. 15/607,410; and Ser. No. 15/607,411; andInternational Application No. PCT/US2017/034848. Each of theseapplications claims benefit of U.S. Provisional Patent Application No.62/401,650, filed Sep. 29, 2016. All of these applications areincorporated by reference herein in their entireties.

TECHNICAL FIELD

The technology disclosed herein relates to fiber lasers andfiber-coupled lasers. More particularly, the disclosed technologyrelates to methods, apparatus, and systems for adjusting and maintainingadjusted optical beam characteristics (spot size, divergence profile,spatial profile, or beam shape, or the like or any combination thereof)at an output of a fiber laser or fiber-coupled laser.

BACKGROUND

The use of high-power fiber-coupled lasers continues to gain popularityfor a variety of applications, such as materials processing, cutting,welding, and/or additive manufacturing. These lasers include, forexample, fiber lasers, disk lasers, diode lasers, diode-pumped solidstate lasers, and lamp-pumped solid state lasers. In these systems,optical power is delivered from the laser to a workpiece via an opticalfiber.

Various fiber-coupled laser materials processing tasks require differentbeam characteristics (e.g., spatial profiles and/or divergenceprofiles). For example, cutting thick metal and welding generallyrequire a larger spot size than cutting thin metal. Ideally, the laserbeam properties would be adjustable to enable optimized processing forthese different tasks. Conventionally, users have two choices: (1)Employ a laser system with fixed beam characteristics that can be usedfor different tasks but is not optimal for most of them (i.e., acompromise between performance and flexibility); or (2) Purchase a lasersystem or accessories that offer variable beam characteristics but thatadd significant cost, size, weight, complexity, and perhaps performancedegradation (e.g., optical loss) or reliability degradation (e.g.,reduced robustness or up-time). Currently available laser systemscapable of varying beam characteristics require the use of free-spaceoptics or other complex and expensive add-on mechanisms (e.g., zoomlenses, mirrors, translatable or motorized lenses, combiners, etc.) inorder to vary beam characteristics. No solution exists that provides thedesired adjustability in beam characteristics that minimizes oreliminates reliance on the use of free-space optics or other extracomponents that add significant penalties in terms of cost, complexity,performance, and/or reliability. What is needed is an in-fiber apparatusfor providing varying beam characteristics that does not require orminimizes the use of free-space optics and that can avoid significantcost, complexity, performance tradeoffs, and/or reliability degradation.

SUMMARY

An optical beam delivery device is formed of optical fibers that areconfigured to produce an output exhibiting an intensity distributionprofile having non-zero ellipticity. The device comprises first andsecond lengths of fiber that are coupled to each other. An incidentoptical beam having beam characteristics propagates through the firstlength of fiber, which has a first refractive index profile (RIP). Thefirst RIP enables, in response to an applied perturbation, modificationof the beam characteristics of the optical beam to form an adjusted beamhaving modified beam characteristics relative to the beamcharacteristics of the optical beam. In disclosed embodiments, the firstRIP comprises a graded index RIP in a radially central portion of thefirst length of fiber. The second length of fiber is formed with a setof one or more confinement regions defining a second RIP and arranged toconfine at least a portion of the adjusted beam to generate, at anoutput of the second length of fiber, an intensity distribution profilehaving non-zero ellipticity.

In some examples of the optical beam delivery device, the set of one ormore confinement regions includes non-coaxial first and secondelliptical confinement regions defining respective first and secondmajor axes. The first and second elliptical confinement regions arespatially offset from each other, and the first and second major axesmay be aligned at an arbitrary angle with each other. In oneimplementation, the first and second major axes are orthogonally alignedrelative to each other.

In some examples of the optical beam delivery device, the set of one ormore confinement regions includes a plurality of non-coaxial circularconfinement regions. Different pairs of closely spaced ones of aplurality of non-coaxial circular confinement regions are orientedcooperatively to generate, at the output of the second length of fiber,the intensity distribution profile having non-zero ellipticity. Indisclosed embodiments, the modified beam characteristics include radialposition of the adjusted beam, and the applied perturbation dithers theradial position of the adjusted beam between confinement regions formingone of the different pairs of closely spaced ones of the plurality ofnon-coaxial circular confinement regions to synthesize the intensitydistribution profile having, on average, non-zero ellipticity. A deviceapplying the perturbation may bend the first length of fiber to positionthe adjusted beam to a location in a two-dimensional plane.

In some examples, the set of one or more confinement regions may includea central confinement region and an elliptical confinement region thatis coaxial with the central confinement region. In disclosedembodiments, the set of one or more confinement regions may include acentral confinement region and first and second elliptical confinementregions that are coaxial with the central confinement region, the firstelliptical confinement region having an outer boundary, and the secondelliptical confinement region having an inner boundary that iscontiguous with the outer boundary of the first elliptical confinementregion.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals representlike elements, are incorporated in and constitute a part of thisspecification and, together with the description, explain the advantagesand principles of the presently disclosed technology. In the drawings,

FIG. 1 illustrates an example fiber structure for providing a laser beamhaving variable beam characteristics;

FIG. 2 depicts a cross-sectional view of an example fiber structure fordelivering a beam with variable beam characteristics;

FIG. 3 illustrates an example method of perturbing a fiber structure forproviding a beam having variable beam characteristics;

FIG. 4 is a graph illustrating the calculated spatial profile of thelowest-order mode (LP₀₁) for a first length of a fiber for differentfiber bend radii;

FIG. 5 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis nearly straight;

FIG. 6 illustrates an example of a two-dimensional intensitydistribution at a junction when a fiber for varying beam characteristicsis bent with a radius chosen to preferentially excite a particularconfinement region of a second length of fiber;

FIGS. 7-10 depict experimental results to illustrate further outputbeams for various bend radii of a fiber for varying beam characteristicsshown in FIG. 2;

FIGS. 11-16 illustrate cross-sectional views of example first lengths offiber for enabling adjustment of beam characteristics in a fiberassembly;

FIGS. 17-19 illustrate cross-sectional views of example second lengthsof fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly;

FIGS. 20 and 21 illustrate cross-sectional views of example secondlengths of fiber for changing a divergence angle of and confining anadjusted beam in a fiber assembly configured to provide variable beamcharacteristics;

FIG. 22A illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and process head;

FIG. 22B illustrates an example a laser system including a fiberassembly configured to provide variable beam characteristics disposedbetween a feeding fiber and process head;

FIG. 23 illustrates an example laser system including a fiber assemblyconfigured to provide variable beam characteristics disposed between afeeding fiber and multiple process fibers;

FIG. 24 illustrates examples of various perturbation assemblies forproviding variable beam characteristics according to various examplesprovided herein;

FIG. 25 illustrates an example process for adjusting and maintainingmodified characteristics of an optical beam;

FIGS. 26-28 are cross-sectional views illustrating example secondlengths of fiber (“confinement fibers”) for confining adjusted beamcharacteristics in a fiber assembly;

FIGS. 29A, 29B, and 29C illustrate a VBC fiber representing anembodiment that is configured to produce an output exhibiting an annularelliptical intensity profile;

FIGS. 30A, 30B, and 30C illustrate a VBC fiber representing anembodiment that is configured to produce an output exhibiting anelliptical intensity profile in different orientations; and

FIGS. 31A, 31B, and 31C illustrate a VBC fiber representing anembodiment that is configured to produce an output exhibiting intensitydistribution profiles having, on average, non-zero ellipticity.

DETAILED DESCRIPTION

As used herein throughout this disclosure and in the claims, thesingular forms “a,” “an,” and “the” include the plural forms unless thecontext clearly dictates otherwise. Additionally, the term “includes”means “comprises.” Further, the term “coupled” does not exclude thepresence of intermediate elements between the coupled items. Also, theterms “modify” and “adjust” are used interchangeably to mean “alter.”

The systems, apparatus, and methods described herein should not beconstrued as limiting in any way. Instead, the present disclosure isdirected toward all novel and non-obvious features and aspects of thevarious disclosed embodiments, alone and in various combinations andsub-combinations with one another. The disclosed systems, methods, andapparatus are not limited to any specific aspect or feature orcombinations thereof, nor do the disclosed systems, methods, andapparatus require that any one or more specific advantages be present orproblems be solved. Any theories of operation are to facilitateexplanation, but the disclosed systems, methods, and apparatus are notlimited to such theories of operation.

Although the operations of some of the disclosed methods are describedin a particular sequential order for convenient presentation, it shouldbe understood that this manner of description encompasses rearrangement,unless a particular ordering is required by specific language set forthbelow. For example, operations described sequentially may in some casesbe rearranged or performed concurrently. Moreover, for the sake ofsimplicity, the attached figures may not show the various ways in whichthe disclosed systems, methods, and apparatus can be used in conjunctionwith other systems, methods, and apparatus. Additionally, thedescription sometimes uses terms like “produce” and “provide” todescribe the disclosed methods. These terms are high-level abstractionsof the actual operations that are performed. The actual operations thatcorrespond to these terms will vary depending on the particularimplementation and are readily discernible by one of ordinary skill inthe art.

In some examples, values, procedures, or apparatus are referred to as“lowest,” “best,” “minimum,” or the like. It will be appreciated thatsuch descriptions are intended to indicate that a selection among manyused functional alternatives can be made, and such selections need notbe better, smaller, or otherwise preferable to other selections.Examples are described with reference to directions indicated as“above,” “below,” “upper,” “lower,” and the like. These terms are usedfor convenient description, but do not imply any particular spatialorientation.

Definitions

Definitions of words and terms as used herein:

1. The term “beam characteristics” refers to one or more of thefollowing terms used to describe an optical beam. In general, the beamcharacteristics of most interest depend on the specifics of theapplication or optical system.2. The term “beam diameter” is defined as the distance across the centerof the beam along an axis for which the irradiance (intensity) equals1/e² of the maximum irradiance. While examples disclosed hereingenerally use beams that propagate in azimuthally symmetric modes,elliptical or other beam shapes can be used, and beam diameter can bedifferent along different axes. Circular beams are characterized by asingle beam diameter. Other beam shapes can have different beamdiameters along different axes.3. The term “spot size” is the radial distance (radius) from the centerpoint of maximum irradiance to the 1/e² point.4. The term “beam divergence distribution” is the power vs the full coneangle. This quantity is sometimes called the “angular distribution” or“NA distribution.”5. The term “beam parameter product” (BPP) of a laser beam is defined asthe product of the beam radius (measured at the beam waist) and the beamdivergence half-angle (measured in the far field). The units of BPP aretypically mm-mrad.6. A “confinement fiber” is defined to be a fiber that possesses one ormore confinement regions, wherein a confinement region comprises ahigher-index region (core region) surrounded by a lower-index region(cladding region). The RIP of a confinement fiber may include one ormore higher-index regions (core regions) surrounded by lower-indexregions (cladding regions), wherein light is guided in the higher-indexregions. Each confinement region and each cladding region can have anyRIP, including but not limited to step-index and graded-index. Theconfinement regions may or may not be concentric and may be a variety ofshapes such as circular, annular, polygonal, arcuate, elliptical, orirregular, or the like or any combination thereof. The confinementregions in a particular confinement fiber may all have the same shape ormay be different shapes. Moreover, confinement regions may be co-axialor may have offset axes with respect to one another. Confinement regionsmay be of uniform thickness about a central axis in the longitudinaldirection, or the thicknesses may vary about the central axis in thelongitudinal direction.7. The term “intensity distribution” refers to optical intensity as afunction of position along a line (1D profile) or on a plane (2Dprofile). The line or plane is usually taken perpendicular to thepropagation direction of the light. It is a quantitative property.8. “Luminance” is a photometric measure of the luminous intensity perunit area of light travelling in a given direction.9. “M² factor” (also called “beam quality factor” or “beam propagationfactor”) is a dimensionless parameter for quantifying the beam qualityof laser beams, with M²=1 being a diffraction-limited beam, and largerM² values corresponding to lower beam quality. M² is equal to the BPPdivided by A/Tr, where A is the wavelength of the beam in microns (ifBPP is expressed in units of mm-mrad).10. The term “numerical aperture” or “NA” of an optical system is adimensionless number that characterizes the range of angles over whichthe system can accept or emit light.11. The term “optical intensity” is not an official (SI) unit, but isused to denote incident power per unit area on a surface or passingthrough a plane.12. The term “power density” refers to optical power per unit area,although this is also referred to as “optical intensity.13. The term “radial beam position” refers to the position of a beam ina fiber measured with respect to the center of the fiber core in adirection perpendicular to the fiber axis.14. “Radiance” is the radiation emitted per unit solid angle in a givendirection by a unit area of an optical source (e.g., a laser). Radiancemay be altered by changing the beam intensity distribution and/or beamdivergence profile or distribution. The ability to vary the radianceprofile of a laser beam implies the ability to vary the BPP.15. The term “refractive-index profile” or “RIP” refers to therefractive index as a function of position along a line (1D) or in aplane (2D) perpendicular to the fiber axis. Many fibers are azimuthallysymmetric, in which case the 1D RIP is identical for any azimuthalangle.16. A “step-index fiber” has a RIP that is flat (refractive indexindependent of position) within the fiber core.17. A “graded-index fiber” has a RIP in which the refractive indexdecreases with increasing radial position (i.e., with increasingdistance from the center of the fiber core).18. A “parabolic-index fiber” is a specific case of a graded-index fiberin which the refractive index decreases quadratically with increasingdistance from the center of the fiber core.

Fiber for Varying Beam Characteristics

Disclosed herein are methods, systems, and apparatus configured toprovide a fiber operable to provide a laser beam having variable beamcharacteristics (VBC) that may reduce cost, complexity, optical loss, orother drawbacks of the conventional methods described above. This VBCfiber is configured to vary a wide variety of optical beamcharacteristics. Such beam characteristics can be controlled using theVBC fiber thus allowing users to tune various beam characteristics tosuit the particular requirements of an extensive variety of laserprocessing applications. For example, a VBC fiber may be used to tunebeam diameter, beam divergence distribution, BPP, intensitydistribution, M² factor, NA, optical intensity, power density, radialbeam position, radiance, spot size, or the like, or any combinationthereof.

In general, the disclosed technology entails coupling a laser beam intoa fiber in which the characteristics of the laser beam in the fiber canbe adjusted by perturbing the laser beam and/or perturbing a firstlength of fiber by any of a variety of methods (e.g., bending the fiberor introducing one or more other perturbations) and fully or partiallymaintaining adjusted beam characteristics in a second length of fiber.The second length of fiber is specially configured to maintain and/orfurther modify the adjusted beam characteristics. In some cases, thesecond length of fiber preserves the adjusted beam characteristicsthrough delivery of the laser beam to its ultimate use (e.g., materialsprocessing). The first and second lengths of fiber may comprise the sameor different fibers.

The disclosed technology is compatible with fiber lasers andfiber-coupled lasers. Fiber-coupled lasers typically deliver an outputvia a delivery fiber having a step-index refractive index profile (RIP),i.e., a flat or constant refractive index within the fiber core. Inreality, the RIP of the delivery fiber may not be perfectly flat,depending on the design of the fiber. Important parameters are the fibercore diameter (d_(core)) and NA. The core diameter is typically in therange of 10-1000 microns (although other values are possible), and theNA is typically in the range of 0.06-0.22 (although other values arepossible). A delivery fiber from the laser may be routed directly to theprocess head or workpiece, or it may be routed to a fiber-to-fibercoupler (FFC) or fiber-to-fiber switch (FFS), which couples the lightfrom the delivery fiber into a process fiber that transmits the beam tothe process head or the workpiece.

Most materials processing tools, especially those at high power (>1 kW),employ multimode (MM) fiber, but some employ single-mode (SM) fiber,which is at the lower end of the d_(core) and NA ranges. The beamcharacteristics from a SM fiber are uniquely determined by the fiberparameters. The beam characteristics from a MM fiber, however, can vary(unit-to-unit and/or as a function of laser power and time), dependingon the beam characteristics from the laser source(s) coupled into thefiber, the launching or splicing conditions into the fiber, the fiberRIP, and the static and dynamic geometry of the fiber (bending, coiling,motion, micro-bending, etc.). For both SM and MM delivery fibers, thebeam characteristics may not be optimum for a given materials processingtask, and it is unlikely to be optimum for a range of tasks, motivatingthe desire to be able to systematically vary the beam characteristics inorder to customize or optimize them for a particular processing task.

In one example, the VBC fiber may have a first length and a secondlength and may be configured to be interposed as an in-fiber devicebetween the delivery fiber and the process head to provide the desiredadjustability of the beam characteristics. To enable adjustment of thebeam, a perturbation device and/or assembly is disposed in closeproximity to and/or coupled with the VBC fiber and is responsible forperturbing the beam in a first length such that the beam'scharacteristics are altered in the first length of fiber, and thealtered characteristics are preserved or further altered as the beampropagates in the second length of fiber. The perturbed beam is launchedinto a second length of the VBC fiber configured to conserve adjustedbeam characteristics. The first and second lengths of fiber may be thesame or different fibers and/or the second length of fiber may comprisea confinement fiber. The beam characteristics that are conserved by thesecond length of VBC fiber may include any of: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity, power density, radial beam position,radiance, spot size, or the like, or any combination thereof.

FIG. 1 illustrates an example VBC fiber 100 for providing a laser beamhaving variable beam characteristics without requiring the use offree-space optics to change the beam characteristics. VBC fiber 100comprises a first length of fiber 104 and a second length of fiber 108.First length of fiber 104 and second length of fiber 108 may be the sameor different fibers and may have the same or different RIPs. The firstlength of fiber 104 and the second length of fiber 108 may be joinedtogether by a splice. First length of fiber 104 and second length offiber 108 may be coupled in other ways, may be spaced apart, or may beconnected via an interposing component such as another length of fiber,free-space optics, glue, index-matching material, or the like or anycombination thereof.

A perturbation device 110 is disposed proximal to and/or envelops aperturbation region 106. Perturbation device 110 may be a device,assembly, in-fiber structure, and/or other feature. Perturbation device110 at least perturbs optical beam 102 in first length of fiber 104 orsecond length of fiber 108 or a combination thereof in order to adjustone or more beam characteristics of optical beam 102. Adjustment of beam102 responsive to perturbation by perturbation device 110 may occur infirst length of fiber 104 or second length of fiber 108 or a combinationthereof. Perturbation region 106 may extend over various widths and mayor may not extend into a portion of second length of fiber 108. As beam102 propagates in VBC fiber 100, perturbation device 110 may physicallyact on VBC fiber 100 to perturb the fiber and adjust the characteristicsof beam 102. Alternatively, perturbation device 110 may act directly onbeam 102 to alter its beam characteristics. Subsequent to beingadjusted, perturbed beam 112 has different beam characteristics fromthose of beam 102, which will be fully or partially conserved in secondlength of fiber 108. In another example, perturbation device 110 neednot be disposed near a splice. Moreover, a splice may not be needed atall, for example VBC fiber 100 may be a single fiber, first length offiber and second length of fiber could be spaced apart, or secured witha small gap (air-spaced or filled with an optical material, such asoptical cement or an index-matching material).

Perturbed beam 112 is launched into second length of fiber 108, whereperturbed beam 112 characteristics are largely maintained or continue toevolve as perturbed beam 112 propagates yielding the adjusted beamcharacteristics at the output of second length of fiber 108. In oneexample, the new beam characteristics may include an adjusted intensitydistribution. In an example, an altered beam intensity distribution willbe conserved in various structurally bounded confinement regions ofsecond length of fiber 108. Thus, the beam intensity distribution may betuned to a desired beam intensity distribution optimized for aparticular laser processing task. In general, the intensity distributionof perturbed beam 112 will evolve as it propagates in the second lengthof fiber 108 to fill the confinement region(s) into which perturbed beam112 is launched responsive to conditions in first length of fiber 104and perturbation caused by perturbation device 110. In addition, theangular distribution may evolve as the beam propagates in the secondfiber, depending on launch conditions and fiber characteristics. Ingeneral, fibers largely preserve the input divergence distribution, butthe distribution can be broadened if the input divergence distributionis narrow and/or if the fiber has irregularities or deliberate featuresthat perturb the divergence distribution. The various confinementregions, perturbations, and fiber features of second length of fiber 108are described in greater detail below. Beams 102 and 112 are conceptualabstractions intended to illustrate how a beam may propagate through aVBC fiber 100 for providing variable beam characteristics and are notintended to closely model the behavior of a particular optical beam.

VBC fiber 100 may be manufactured by a variety of methods including PCVD(Plasma Chemical Vapor Deposition), OVD (Outside Vapor Deposition), VAD(Vapor Axial Deposition), MOCVD (Metal-Organic Chemical VaporDeposition.) and/or DND (Direct Nanoparticle Deposition). VBC fiber 100may comprise a variety of materials. For example, VBC fiber 100 maycomprise SiO₂, SiO₂ doped with GeO₂, germanosilicate, phosphoruspentoxide, phosphosilicate, Al₂O₃, aluminosilicate, or the like or anycombinations thereof. Confinement regions may be bounded by claddingdoped with fluorine, boron, or the like or any combinations thereof.Other dopants may be added to active fibers, including rare-earth ionssuch as Er³⁺ (erbium), Yb³⁺ (ytterbium), Nd³⁺ (neodymium), Tm³⁺(thulium), Ho³⁺ (holmium), or the like or any combination thereof.Confinement regions may be bounded by cladding having a lower index thanthat of the confinement region with fluorine or boron doping.Alternatively, VBC fiber 100 may comprise photonic crystal fibers ormicro-structured fibers.

VBC fiber 100 is suitable for use in any of a variety of fiber, fiberoptic, or fiber laser devices, including continuous wave and pulsedfiber lasers, disk lasers, solid state lasers, or diode lasers (pulserate unlimited except by physical constraints). Furthermore,implementations in a planar waveguide or other types of waveguides andnot just fibers are within the scope of the claimed technology.

FIG. 2 depicts a cross-sectional view of an example VBC fiber 200 foradjusting beam characteristics of an optical beam. In an example, VBCfiber 200 may be a process fiber because it may deliver the beam to aprocess head for material processing. VBC fiber 200 comprises a firstlength of fiber 204 spliced at a junction 206 to a second length offiber 208. A perturbation assembly 210 is disposed proximal to junction206. Perturbation assembly 210 may be any of a variety of devicesconfigured to enable adjustment of the beam characteristics of anoptical beam 202 propagating in VBC fiber 200. In an example,perturbation assembly 210 may be a mandrel and/or another device thatmay provide means of varying the bend radius and/or bend length of VBCfiber 200 near the splice. Other examples of perturbation devices arediscussed below with respect to FIG. 24.

In an example, first length of fiber 204 has a parabolic-index RIP 212as indicated by the left RIP graph. Most of the intensity distributionof beam 202 is concentrated in the center of fiber 204 when fiber 204 isstraight or nearly straight. Second length of fiber 208 is a confinementfiber having RIP 214 as shown in the right RIP graph. Second length offiber 208 includes confinement regions 216, 218, and 220. Confinementregion 216 is a central core surrounded by two annular (or ring-shaped)confinement regions 218 and 220. Layers 222 and 224 are structuralbarriers of lower index material between confinement regions (216, 218and 220), commonly referred to as “cladding” regions. In one example,layers 222 and 224 may comprise rings of fluorosilicate; in someembodiments, the fluorosilicate cladding layers are relatively thin.Other materials may be used as well, and claimed subject matter is notlimited in this regard.

In an example, as beam 202 propagates along VBC fiber 200, perturbationassembly 210 may physically act on fiber 204 and/or beam 202 to adjustits beam characteristics and generate an adjusted beam 226. In thecurrent example, the intensity distribution of beam 202 is modified byperturbation assembly 210. Subsequent to adjustment of beam 202, theintensity distribution of adjusted beam 226 may be concentrated in outerconfinement regions 218 and 220 with relatively little intensity in thecentral confinement region 216. Because each of confinement regions 216,218, and/or 220 is isolated by the thin layers of lower index materialin barrier layers 222 and 224, second length of fiber 208 cansubstantially maintain the adjusted intensity distribution of adjustedbeam 226. The beam will typically become distributed azimuthally withina given confinement region but will not transition (significantly)between the confinement regions as it propagates along the second lengthof fiber 208. Thus, the adjusted beam characteristics of adjusted beam226 are largely conserved within the isolated confinement regions 216,218, and/or 220. In some cases, it be may desirable to have the beam 226power divided among the confinement regions 216, 218, and/or 220 ratherthan concentrated in a single region, and this condition may be achievedby generating an appropriately adjusted beam 226.

In one example, core confinement region 216 and annular confinementregions 218 and 220 may be composed of fused silica glass, and cladding222 and 224 defining the confinement regions may be composed offluorosilicate glass. Other materials may be used to form the variousconfinement regions (216, 218 and 220), including germanosilicate,phosphosilicate, aluminosilicate, or the like, or a combination thereofand claimed subject matter is not so limited. Other materials may beused to form the barrier rings (222 and 224), including fused silica,borosilicate, or the like or a combination thereof, and claimed subjectmatter is not so limited. In other embodiments, the optical fibers orwaveguides include or are composed of various polymers or plastics orcrystalline materials. Generally, the core confinement regions haverefractive indices that are greater than the refractive indices ofadjacent barrier/cladding regions.

In some examples, it may be desirable to increase a number ofconfinement regions in a second length of fiber to increase granularityof beam control over beam displacements for fine-tuning a beam profile.For example, confinement regions may be configured to provide stepwisebeam displacement.

FIG. 3 illustrates an example method of perturbing fiber 200 forproviding variable beam characteristics of an optical beam. Changing thebend radius of a fiber may change the radial beam position, divergenceangle, and/or radiance profile of a beam within the fiber. The bendradius of VBC fiber 200 can be decreased from a first bend radius R₁ toa second bend radius R₂ about splice junction 206 by using a steppedmandrel or cone as the perturbation assembly 210. Additionally oralternatively, the engagement length on the mandrel(s) or cone can bevaried. Rollers 250 may be employed to engage VBC fiber 200 acrossperturbation assembly 210. In an example, an amount of engagement ofrollers 250 with fiber 200 has been shown to shift the distribution ofthe intensity profile to the outer confinement regions 218 and 220 offiber 200 with a fixed mandrel radius. There are a variety of othermethods for varying the bend radius of fiber 200, such as using aclamping assembly, flexible tubing, or the like, or a combinationthereof, and claimed subject matter is not limited in this regard. Inanother example, for a particular bend radius the length over which VBCfiber 200 is bent can also vary beam characteristics in a controlled andreproducible way. In examples, changing the bend radius and/or lengthover which the fiber is bent at a particular bend radius also modifiesthe intensity distribution of the beam such that one or more modes maybe shifted radially away from the center of a fiber core.

Maintaining the bend radius of the fibers across junction 206 ensuresthat the adjusted beam characteristics such as radial beam position andradiance profile of optical beam 202 will not return to its unperturbedstate before being launched into second length of fiber 208. Moreover,the adjusted radial beam characteristics, including position, divergenceangle, and/or intensity distribution, of adjusted beam 226 can be variedbased on an extent of decrease in the bend radius and/or the extent ofthe bent length of VBC fiber 200. Thus, specific beam characteristicsmay be obtained using this method.

In the current example, first length of fiber 204 having first RIP 212is spliced at junction 206 to a second length of fiber 208 having asecond RIP 214. However, it is possible to use a single fiber having asingle RIP formed to enable perturbation (e.g., by micro-bending) of thebeam characteristics of beam 202 and to enable conservation of theadjusted beam. Such a RIP may be similar to the RIPs shown in fibersillustrated in FIGS. 17, 18, and/or 19.

FIGS. 7-10 provide experimental results for VBC fiber 200 (shown inFIGS. 2 and 3) and illustrate further a beam response to perturbation ofVBC fiber 200 when a perturbation assembly 210 acts on VBC fiber 200 tobend the fiber. FIGS. 4-6 are simulations and FIGS. 7-10 areexperimental results wherein a beam from a SM 1050 nm source waslaunched into an input fiber (not shown) with a 40 micron core diameter.The input fiber was spliced to first length of fiber 204.

FIG. 4 is an example graph 400 illustrating the calculated profile ofthe lowest-order mode (LP₀₁) for a first length of fiber 204 fordifferent fiber bend radii 402, wherein a perturbation assembly 210involves bending VBC fiber 200. As the fiber bend radius is decreased,an optical beam propagating in VBC fiber 200 is adjusted such that themode shifts radially away from the center 404 of a VBC fiber 200 core(r=0 micron) toward the core/cladding interface (located at r=100 micronin this example). Higher-order modes (LP_(In)) also shift with bending.Thus, for a straight or nearly straight fiber (very large bend radius),curve 406 for LP₀₁ is centered at or near the center of VBC fiber 200.At a bend radius of about 6 cm, curve 408 for LP₀₁ is shifted to aradial position of about 40 μm from the center 406 of VBC fiber 200. Ata bend radius of about 5 cm, curve 410 for LP₀₁ is shifted to a radialposition about 50 μm from the center 406 of VBC fiber 200. At a bendradius of about 4 cm, curve 412 for LP₀₁ is shifted to a radial positionabout 60 μm from the center 406 of VBC fiber 200. At a bend radius ofabout 3 cm, curve 414 for LP₀₁ is shifted to a radial position about 80μm from the center 406 of VBC fiber 200. At a bend radius of about 2.5cm, a curve 416 for LP₀₁ is shifted to a radial position about 85 μmfrom the center 406 of VBC fiber 200. Note that the shape of the moderemains relatively constant (until it approaches the edge of the core),which is a specific property of a parabolic RIP. Although, this propertymay be desirable in some situations, it is not required for the VBCfunctionality, and other RIPs may be employed.

In an example, if VBC fiber 200 is straightened, LP₀₁ mode will shiftback toward the center of the fiber. Thus, the purpose of second lengthof fiber 208 is to “trap” or confine the adjusted intensity distributionof the beam in a confinement region that is displaced from the center ofthe VBC fiber 200. The splice between fibers 204 and 208 is included inthe bent region, thus the shifted mode profile will be preferentiallylaunched into one of the ring-shaped confinement regions 218 and 220 orbe distributed among the confinement regions. FIGS. 5 and 6 illustratethis effect.

FIG. 5 illustrates an example of two-dimensional intensity distributionat junction 206 within second length of fiber 208 when VBC fiber 200 isnearly straight. A significant portion of LP₀₁ and LP_(In) is withinconfinement region 216 of fiber 208. FIG. 6 illustrates thetwo-dimensional intensity distribution at junction 206 within secondlength of fiber 208 when VBC fiber 200 is bent with a radius chosen topreferentially excite confinement region 220 (the outermost confinementregion) of second length of fiber 208. A significant portion of LP₀₁ andLP_(In) is within confinement region 220 of fiber 208.

In an example, in second length of fiber 208, confinement region 216 hasa 100 micron diameter, confinement region 218 is between 120 micron and200 micron in diameter, and confinement region 220 is between 220 micronand 300 micron diameter. Confinement regions 216, 218, and 220 areseparated by 10 μm thick rings of fluorosilicate, providing an NA of0.22 for the confinement regions. Other inner and outer diameters forthe confinement regions, thicknesses of the rings separating theconfinement regions, NA values for the confinement regions, and numbersof confinement regions may be employed.

Referring again to FIG. 5, with the noted parameters, when VBC fiber 200is straight, about 90% of the power is contained within the centralconfinement region 216, and about 100% of the power is contained withinconfinement regions 216 and 218. Referring now to FIG. 6, when fiber 200is bent to preferentially excite second ring confinement region 220,nearly 75% of the power is contained within confinement region 220, andmore than 95% of the power is contained within confinement regions 218and 220. These calculations include LP₀₁ and two higher-order modes,which are typical in some 2-4 kW fiber lasers.

It is clear from FIGS. 5 and 6 that, in the case where a perturbationassembly 210 acts on VBC fiber 200 to bend the fiber, the bend radiusdetermines the spatial overlap of the modal intensity distribution ofthe first length of fiber 204 with the different guiding confinementregions (216, 218, and 220) of the second length of fiber 208. Changingthe bend radius can thus change the intensity distribution at the outputof the second length of fiber 208, thereby changing the diameter or spotsize of the beam, and thus changing its radiance and BPP value. Thisadjustment of the spot size may be accomplished in an all-fiberstructure, involving no free-space optics and consequently may reduce oreliminate the disadvantages of free-space optics discussed above. Suchadjustments can also be made with other perturbation assemblies thatalter bend radius, bend length, fiber tension, temperature, or otherperturbations discussed below.

In a typical materials processing system (e.g., a cutting or weldingtool), the output of the process fiber is imaged at or near theworkpiece by the process head. Varying the intensity distribution asshown in FIGS. 5 and 6 thus enables variation of the beam profile at theworkpiece in order to tune and/or optimize the process, as desired.Specific RIPs for the two fibers were assumed for the purpose of theabove calculations, but other RIPs are possible, and claimed subjectmatter is not limited in this regard.

FIGS. 7-10 depict experimental results (measured intensitydistributions) to illustrate further output beams for various bend radiiof VBC fiber 200 shown in FIG. 2.

In FIG. 7 when VBC fiber 200 is straight, the beam is nearly completelyconfined to confinement region 216. As the bend radius is decreased, theintensity distribution shifts to higher diameters (FIGS. 8-10). FIG. 8depicts the intensity distribution when the bend radius of VBC fiber 200is chosen to shift the intensity distribution preferentially toconfinement region 218. FIG. 9 depicts the experimental results when thebend radius is further reduced and chosen to shift the intensitydistribution outward to confinement region 220 and confinement region218. In FIG. 10, at the smallest bend radius, the beam is nearly a“donut mode,” with most of the intensity in the outermost confinementregion 220.

Despite excitation of the confinement regions from one side at thesplice junction 206, the intensity distributions are nearly symmetricazimuthally because of scrambling within confinement regions as the beampropagates within the VBC fiber 200. Although the beam will typicallyscramble azimuthally as it propagates, various structures orperturbations (e.g., coils) could be included to facilitate thisprocess.

For the fiber parameters used in the experiment shown in FIGS. 7-10,particular confinement regions were not exclusively excited because someintensity was present in multiple confinement regions. This feature mayenable advantageous materials processing applications that are optimizedby having a flatter or distributed beam intensity distribution. Inapplications requiring cleaner excitation of a given confinement region,different fiber RIPs could be employed to enable this feature.

The results shown in FIGS. 7-10 pertain to the particular fibers used inthis experiment, and the details will vary depending on the specifics ofthe implementation. In particular, the spatial profile and divergencedistribution of the output beam and their dependence on bend radius willdepend on the specific RIPs employed, on the splice parameters, and onthe characteristics of the laser source launched into the first fiber.

Different fiber parameters from those shown in FIG. 2 may be used andstill be within the scope of the claimed subject matter. Specifically,different RIPs and core sizes and shapes may be used to facilitatecompatibility with different input beam profiles and to enable differentoutput beam characteristics. Example RIPs for the first length of fiber,in addition to the parabolic-index profile shown in FIG. 2, includeother graded-index profiles, step-index, pedestal designs (i.e., nestedcores with progressively lower refractive indices with increasingdistance from the center of the fiber), and designs with nested coreswith the same refractive index value but with various NA values for thecentral core and the surrounding rings. Example RIPs for the secondlength of fiber, in addition to the profile shown in FIG. 2, includeconfinement fibers with different numbers of confinement regions,non-uniform confinement-region thicknesses, different and/or non-uniformvalues for the thicknesses of the rings surrounding the confinementregions, different and/or non-uniform NA values for the confinementregions, different refractive-index values for the high-index andlow-index portions of the RIP, non-circular confinement regions (such aselliptical, oval, polygonal, square, rectangular, or combinationsthereof), as well as other designs as discussed in further detail withrespect to FIGS. 26-28. Furthermore, VBC fiber 200 and other examples ofa VBC fiber described herein are not restricted to use of two fibers. Insome examples, implementation may include use of one fiber or more thantwo fibers. In some cases, the fiber(s) may not be axially uniform; forexample, they could include fiber Bragg gratings or long-periodgratings, or the diameter could vary along the length of the fiber. Inaddition, the fibers do not have to be azimuthally symmetric, e.g., thecore(s) could have square or polygonal shapes. Various fiber coatings(buffers) may be employed, including high-index or index-matchedcoatings (which strip light at the glass-polymer interface) andlow-index coatings (which guide light by total internal reflection atthe glass-polymer interface). In some examples, multiple fiber coatingsmay be used on VBC fiber 200.

FIGS. 11-16 illustrate cross-sectional views of examples of firstlengths of fiber for enabling adjustment of beam characteristics in aVBC fiber responsive to perturbation of an optical beam propagating inthe first lengths of fiber. Some examples of beam characteristics thatmay be adjusted in the first length of fiber are: beam diameter, beamdivergence distribution, BPP, intensity distribution, luminance, M²factor, NA, optical intensity profile, power density profile, radialbeam position, radiance, spot size, or the like, or any combinationthereof. The first lengths of fiber depicted in FIGS. 11-16 anddescribed below are merely examples and do not provide an exhaustiverecitation of the variety of first lengths of fiber that may be utilizedto enable adjustment of beam characteristics in a VBC fiber assembly.Selection of materials, appropriate RIPs, and other variables for thefirst lengths of fiber illustrated in FIGS. 11-16 at least depend on adesired beam output. A wide variety of fiber variables are contemplatedand are within the scope of the claimed subject matter. Thus, claimedsubject matter is not limited by examples provided herein.

In FIG. 11 first length of fiber 1100 comprises a step-index profile1102. FIG. 12 illustrates a first length of fiber 1200 comprising a“pedestal RIP” (i.e., a core comprising a step-index region surroundedby a larger step-index region) 1202. FIG. 13 illustrates a first lengthof fiber 1300 comprising a multiple-pedestal RIP 1302.

FIG. 14A illustrates a first length of fiber 1400 comprising agraded-index profile 1418 surrounded by a down-doped region 1404. Whenthe fiber 1400 is perturbed, modes may shift radially outward in fiber1400 (e.g., during bending of fiber 1400). Graded-index profile 1402 maybe designed to promote maintenance or even compression of modal shape.This design may promote adjustment of a beam propagating in fiber 1400to generate a beam having a beam intensity distribution concentrated inan outer perimeter of the fiber (i.e., in a portion of the fiber corethat is displaced from the fiber axis). As described above, when theadjusted beam is coupled into a second length of fiber havingconfinement regions, the intensity distribution of the adjusted beam maybe trapped in the outermost confinement region, providing a donut shapedintensity distribution. A beam spot having a narrow outer confinementregion may be useful to enable certain material processing actions.

FIG. 14B illustrates a first length of fiber 1406 comprising agraded-index profile 1414 surrounded by a down-doped region 1408 similarto that of fiber 1400. However, fiber 1406 includes a divergencestructure 1410 (a lower-index region) as can be seen in profile 1412.The divergence structure 1410 is an area of material with a lowerrefractive index than that of the surrounding core. As the beam islaunched into first length of fiber 1406, refraction from divergencestructure 1410 causes the beam divergence to increase in first length offiber 1406. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure 1410 and themagnitude of the index difference between the divergence structure 1410and the core material. Divergence structure 1410 can have a variety ofshapes, depending on the input divergence distribution and desiredoutput divergence distribution. In an example, divergence structure 1410has a triangular or graded index shape.

FIG. 15 illustrates a first length of fiber 1500 comprising aparabolic-index central region 1502 surrounded by a constant-indexregion 1504. Between the constant-index region 1504 and theparabolic-index central region 1502 is a lower-index annular layer (orlower-index ring or annulus) 1506 surrounding the parabolic-indexcentral region 1502. The lower-index annulus 1506 helps guide a beampropagating in fiber 1500. When the propagating beam is perturbed, modesshift radially outward in fiber 1500 (e.g., during bending of fiber1500). As one or more modes shift radially outward, parabolic-indexregion 1502 promotes retention of modal shape. When the modes reach theconstant-index region 1504 at outer portions of a RIP 1510, they will becompressed against the lower-index ring 1506, which (in comparison tothe first fiber RIP shown in FIGS. 14A and 14B) may cause preferentialexcitation of the outermost confinement region in the second fiber. Inone implementation, this fiber design works with a confinement fiberhaving a central step-index core and a single annular core. Theparabolic-index portion 1502 of the RIP 1510 overlaps with the centralstep-index core of the confinement fiber. The constant-index portion1504 overlaps with the annular core of the confinement fiber. Theconstant-index portion 1504 of the first fiber is intended to make iteasier to move the beam into overlap with the annular core by bending.This fiber design also works with other designs of the confinementfiber.

FIG. 16 illustrates a first length of fiber 1600 comprising guidingregions 1604, 1606, 1608, and 1616 bounded by lower-index layers 1610,1612, and 1614 where the indexes of the lower-index layers 1610, 1612,and 1614 are stepped or, more generally, do not all have the same value.The stepped-index layers may serve to bound the beam intensity tocertain guiding regions (1604, 1606, 1608, and 1616) when theperturbation assembly 210 (see FIG. 2) acts on the fiber 1600. In thisway, adjusted beam light may be trapped in the guiding regions over arange of perturbation actions (such as over a range of bend radii, arange of bend lengths, a range of micro-bending pressures, and/or arange of acousto-optical signals), allowing for a certain degree ofperturbation tolerance before a beam intensity distribution is shiftedto a more distant radial position in fiber 1600. Thus, variation in beamcharacteristics may be controlled in a step-wise fashion. The radialwidths of the guiding regions 1604, 1606, 1608, and 1616 may be adjustedto achieve a desired ring width, as may be required by an application.Also, a guiding region can have a thicker radial width to facilitatetrapping of a larger fraction of the incoming beam profile if desired.Region 1606 is an example of such a design.

FIGS. 17-21 depict examples of fibers configured to enable maintenanceand/or confinement of adjusted beam characteristics in the second lengthof fiber (e.g., fiber 208). These fiber designs are referred to as“ring-shaped confinement fibers” because they contain a central coresurrounded by annular or ring-shaped cores. These designs are merelyexamples and not an exhaustive recitation of the variety of fiber RIPsthat may be used to enable maintenance and/or confinement of adjustedbeam characteristics within a fiber. Thus, claimed subject matter is notlimited to the examples provided herein. Moreover, any of the firstlengths of fiber described above with respect to FIGS. 11-16 may becombined with any of the second length of fiber described FIGS. 17-21.

FIG. 17 illustrates a cross-sectional view of an example second lengthof fiber for maintaining and/or confining adjusted beam characteristicsin a VBC fiber assembly. As the perturbed beam is coupled from a firstlength of fiber to a second length of fiber 1700, the second length offiber 1700 may maintain at least a portion of the beam characteristicsadjusted in response to perturbation in the first length of fiber withinone or more of confinement regions 1704, 1706, and/or 1708. Fiber 1700has a RIP 1702. Each of confinement regions 1704, 1706, and/or 1708 isbounded by a lower index layer 1710 and/or 1712. This design enablessecond length of fiber 1700 to maintain the adjusted beamcharacteristics. As a result, a beam output by fiber 1700 willsubstantially maintain the received adjusted beam as modified in thefirst length of fiber giving the output beam adjusted beamcharacteristics, which may be customized to a processing task or otherapplication.

Similarly, FIG. 18 depicts a cross-sectional view of an example secondlength of fiber 1800 for maintaining and/or confining beamcharacteristics adjusted in response to perturbation in the first lengthof fiber in a VBC fiber assembly. Fiber 1800 has a RIP 1802. However,confinement regions 1808, 1810, and/or 1812 have different thicknessesfrom the thicknesses of confinement regions 1704, 1706, and 1708. Eachof confinement regions 1808, 1810, and/or 1812 is bounded by a lowerindex layer 1804 and/or 1806. Varying the thicknesses of the confinementregions (and/or barrier regions) enables tailoring or optimization of aconfined adjusted radiance profile by selecting particular radialpositions within which to confine an adjusted beam.

FIG. 19 depicts a cross-sectional view of an example second length offiber 1900 having a RIP 1902 for maintaining and/or confining anadjusted beam in a VBC fiber assembly configured to provide variablebeam characteristics. In this example, the number and thicknesses ofconfinement regions 1904, 1906, 1908, and 1910 are different from thoseof fiber 1700 and 1800; and the barrier layers 1912, 1914, and 1916 areof varied thicknesses as well. Furthermore, confinement regions 1904,1906, 1908, and 1910 have different indexes of refraction; and barrierlayers 1912, 1914, and 1916 have different indexes of refraction aswell. This design may further enable a more granular or optimizedtailoring of the confinement and/or maintenance of an adjusted beamradiance to particular radial locations within fiber 1900. As theperturbed beam is launched from a first length of fiber to second lengthof fiber 1900, the modified beam characteristics of the beam (having anadjusted intensity distribution, radial position, and/or divergenceangle, or the like, or a combination thereof) is confined within aspecific radius by one or more of confinement regions 1904, 1906, 1908,and/or 1910 of second length of fiber 1900.

As noted previously, the divergence angle of a beam may be conserved oradjusted and then conserved in the second length of fiber. There are avariety of methods to change the divergence angle of a beam. Thefollowing are examples of fibers configured to enable adjustment of thedivergence angle of a beam propagating from a first length of fiber to asecond length of fiber in a fiber assembly for varying beamcharacteristics. However, these are merely examples and not anexhaustive recitation of the variety of methods that may be used toenable adjustment of divergence of a beam. Thus, claimed subject matteris not limited to the examples provided herein.

FIG. 20 depicts a cross-sectional view of an example second length offiber 2000 having a RIP 2002 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. In this example, second length of fiber 2000is similar to the previously described second lengths of fiber and formsa portion of the VBC fiber assembly for delivering variable beamcharacteristics as discussed above. There are three confinement regions2004, 2006, and 2008 and three barrier layers 2010, 2012, and 2016.Second length of fiber 2000 also has a divergence structure 2014situated within the confinement region 2006. The divergence structure2014 is an area of material with a lower refractive index than that ofthe surrounding confinement region. As the beam is launched into secondlength of fiber 2000, refraction from divergence structure 2014 causesthe beam divergence to increase in second length of fiber 2000. Theamount of increased divergence depends on the amount of spatial overlapof the beam with the divergence structure 2014 and the magnitude of theindex difference between the divergence structure 2014 and the corematerial. By adjusting the radial position of the beam near the launchpoint into the second length of fiber 2000, the divergence distributionmay be varied. The adjusted divergence of the beam is conserved in fiber2000, which is configured to deliver the adjusted beam to the processhead, another optical system (e.g., fiber-to-fiber coupler orfiber-to-fiber switch), the workpiece, or the like, or a combinationthereof. In an example, divergence structure 2014 may have an index dipof about 10⁻⁵-3×10⁻² with respect to the surrounding material. Othervalues of the index dip may be employed within the scope of thisdisclosure, and claimed subject matter is not so limited.

FIG. 21 depicts a cross-sectional view of an example second length offiber 2100 having a RIP 2102 for modifying, maintaining, and/orconfining beam characteristics adjusted in response to perturbation inthe first length of fiber. Second length of fiber 2100 forms a portionof a VBC fiber assembly for delivering a beam having variablecharacteristics. In this example, there are three confinement regions2104, 2106, and 2108 and three barrier layers 2110, 2112, and 2116.Second length of fiber 2100 also has a plurality of divergencestructures 2114 and 2118. The divergence structures 2114 and 2118 areareas of graded lower index material. As the beam is launched from thefirst length fiber into second length of fiber 2100, refraction fromdivergence structures 2114 and 2118 causes the beam divergence toincrease. The amount of increased divergence depends on the amount ofspatial overlap of the beam with the divergence structure and themagnitude of the index difference between the divergence structure 2114and/or 2118 and the surrounding core material of confinement regions2106 and 2104 respectively. By adjusting the radial position of the beamnear the launch point into the second length of fiber 2100, thedivergence distribution may be varied. The design shown in FIG. 21allows the intensity distribution and the divergence distribution to bevaried somewhat independently by selecting both a particular confinementregion and the divergence distribution within that confinement region(because each confinement region may include a divergence structure).The adjusted divergence of the beam is conserved in fiber 2100, which isconfigured to deliver the adjusted beam to the process head, anotheroptical system, or the workpiece. Forming the divergence structures 2114and 2118 with a graded or non-constant index enables tuning of thedivergence profile of the beam propagating in fiber 2100. An adjustedbeam characteristic such as a radiance profile and/or divergence profilemay be conserved as it is delivered to a process head by the secondfiber. Alternatively, an adjusted beam characteristic such as a radianceprofile and/or divergence profile may be conserved or further adjustedas it is routed by the second fiber through a fiber-to-fiber coupler(FFC) and/or fiber-to-fiber switch (FFS) and to a process fiber, whichdelivers the beam to the process head or the workpiece.

FIGS. 26-28 are cross-sectional views illustrating examples of fibersand fiber RIPs configured to enable maintenance and/or confinement ofadjusted beam characteristics of a beam propagating in an azimuthallyasymmetric second length of fiber, wherein the beam characteristics areadjusted responsive to perturbation of a first length of fiber coupledto the second length of fiber and/or perturbation of the beam by aperturbation device 110. These azimuthally asymmetric designs are merelyexamples and are not an exhaustive recitation of the variety of fiberRIPs that may be used to enable maintenance and/or confinement ofadjusted beam characteristics within an azimuthally asymmetric fiber.Thus, claimed subject matter is not limited to the examples providedherein. Moreover, any of a variety of first lengths of fiber (e.g., likethose described above) may be combined with any azimuthally asymmetricsecond length of fiber (e.g., like those described in FIGS. 26-28).

FIG. 26 illustrates RIPs at various azimuthal angles of a cross-sectionthrough an elliptical fiber 2600. At a first azimuthal angle 2602, fiber2600 has a first RIP 2604. At a second azimuthal angle 2606 that isrotated 45° from first azimuthal angle 2602, fiber 2600 has a second RIP2608. At a third azimuthal angle 2610 that is rotated another 45° fromsecond azimuthal angle 2606, fiber 2600 has a third RIP 2612. First,second, and third RIPs 2604, 2608, and 2612 are all different.

FIG. 27 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a multi-core fiber 2700. At a first azimuthal angle 2702, fiber2700 has a first RIP 2704. At a second azimuthal angle 2706, fiber 2700has a second RIP 2708. First and second RIPs 2704 and 2708 aredifferent. In an example, perturbation device 110 may act in multipleplanes in order to launch the adjusted beam into different regions of anazimuthally asymmetric second fiber.

FIG. 28 illustrates RIPs at various azimuthal angles of a cross-sectionthrough a fiber 2800 having at least one crescent shaped core. In somecases, the corners of the crescent may be rounded, flattened, orotherwise shaped, which may minimize optical loss. At a first azimuthalangle 2802, fiber 2800 has a first RIP 2804. At a second azimuthal angle2806, fiber 2800 has a second RIP 2808. First and second RIPs 2804 and2808 are different.

FIG. 22A illustrates an example of a laser system 2200 including a VBCfiber assembly 2202 configured to provide variable beam characteristics.VBC fiber assembly 2202 comprises a first length of fiber 104, a secondlength of fiber 108, and a perturbation device 110. VBC fiber assembly2202 is disposed between feeding fiber 2212 (i.e., the output fiber fromthe laser source) and VBC delivery fiber 2240. VBC delivery fiber 2240may comprise second length of fiber 108 or an extension of second lengthof fiber 108 that modifies, maintains, and/or confines adjusted beamcharacteristics. Beam 2210 is coupled into VBC fiber assembly 2202 viafeeding fiber 2212. Fiber assembly 2202 is configured to vary thecharacteristics of beam 2210 in accordance with the various examplesdescribed above. The output of fiber assembly 2202 is adjusted beam2214, which is coupled into VBC delivery fiber 2240. VBC delivery fiber2240 delivers adjusted beam 2214 to a free-space optics assembly 2208,which then couples beam 2214 into a process fiber 2204. Adjusted beam2214 is then delivered to process head 2206 by process fiber 2204. Theprocess head can include guided wave optics (such as fibers and fibercoupler), free space optics (such as lenses, mirrors, optical filters,diffraction gratings), and/or beam scan assemblies (such as galvanometerscanners, polygonal mirror scanners, or other scanning systems) that areused to shape the beam 2214 and deliver the shaped beam to a workpiece.

In laser system 2200, one or more of the free-space optics of assembly2208 may be disposed in an FFC or other beam coupler 2216 to perform avariety of optical manipulations of an adjusted beam 2214 (representedin FIG. 22A with different dashing from that of beam 2210). For example,free-space optics assembly 2208 may preserve the adjusted beamcharacteristics of beam 2214. Process fiber 2204 may have the same RIPas VBC delivery fiber 2240. Thus, the adjusted beam characteristics ofadjusted beam 2214 may be preserved all the way to process head 2206.Process fiber 2204 may comprise a RIP similar to any of the secondlengths of fiber described above, including confinement regions.

Alternatively, as illustrated in FIG. 22B, free-space optics assembly2208 may change the adjusted beam characteristics of beam 2214 by, forexample, increasing or decreasing the divergence and/or the spot size ofbeam 2214 (e.g., by magnifying or demagnifying beam 2214) and/orotherwise further modifying adjusted beam 2214. Furthermore, processfiber 2204 may have a different RIP than VBC delivery fiber 2240.Accordingly, the RIP of process fiber 2204 may be selected to preserveadditional adjustment of adjusted beam 2214 made by the free-spaceoptics of assembly 2208 to generate a twice adjusted beam 2224(represented in FIG. 22B with different dashing from that of beam 2214).

FIG. 23 illustrates an example of a laser system 2300 including VBCfiber assembly 2302 disposed between a feeding fiber 2312 and a VBCdelivery fiber 2340. During operation, a beam 2310 is coupled into VBCfiber assembly 2302 via feeding fiber 2312. Fiber assembly 2302 includesa first length of fiber 104, a second length of fiber 108, and aperturbation device 110 and is configured to vary characteristics ofbeam 2310 in accordance with the various examples described above. Fiberassembly 2302 generates an adjusted beam 2314 output by VBC deliveryfiber 2340. VBC delivery fiber 2340 comprises a second length of fiber108 of fiber for modifying, maintaining, and/or confining adjusted beamcharacteristics in a fiber assembly 2302 in accordance with the variousexamples described above (see FIGS. 17-21, for example). VBC deliveryfiber 2340 couples adjusted beam 2314 into a beam switch (FFS) 2332,which then couples its various output beams to one or more of multipleprocess fibers 2304, 2320, and 2322. Process fibers 2304, 2320, and 2322deliver adjusted beams 2314, 2328, and 2330 to respective process heads2306, 2324, and 2326.

In an example, beam switch 2332 includes one or more sets of free-spaceoptics 2308, 2316, and 2318 configured to perform a variety of opticalmanipulations of adjusted beam 2314. Free-space optics 2308, 2316, and2318 may preserve or vary adjusted beam characteristics of beam 2314.Thus, adjusted beam 2314 may be maintained by the free-space optics oradjusted further. Process fibers 2304, 2320, and 2322 may have the sameor a different RIP as that of VBC delivery fiber 2340, depending onwhether it is desirable to preserve or further modify a beam passingfrom the free-space optics assemblies 2308, 2316, and 2318 to respectiveprocess fibers 2304, 2320, and 2322. In other examples, one or more beamportions of beam 2310 are coupled to a workpiece without adjustment, ordifferent beam portions are coupled to respective VBC fiber assembliesso that beam portions associated with a plurality of beamcharacteristics can be provided for simultaneous workpiece processing.Alternatively, beam 2310 can be switched to one or more of a set of VBCfiber assemblies.

Routing adjusted beam 2314 through any of free-space optics assemblies2308, 2316, and 2318 enables delivery of a variety of additionallyadjusted beams to process heads 2206, 2324, and 2326. Therefore, lasersystem 2300 provides additional degrees of freedom for varying thecharacteristics of a beam, as well as switching the beam between processheads (“time sharing”) and/or delivering the beam to multiple processheads simultaneously (“power sharing”).

For example, free-space optics in beam switch 2332 may direct adjustedbeam 2314 to free-space optics assembly 2316 configured to preserve theadjusted characteristics of beam 2314. Process fiber 2304 may have thesame RIP as that of VBC delivery fiber 2340. Thus, the beam delivered toprocess head 2306 will be a preserved adjusted beam 2314.

In another example, beam switch 2332 may direct adjusted beam 2314 tofree-space optics assembly 2318 configured to preserve the adjustedcharacteristics of adjusted beam 2314. Process fiber 2320 may have adifferent RIP from that of VBC delivery fiber 2340 and may be configuredwith divergence altering structures as described with respect to FIGS.20 and 21 to provide additional adjustments to the divergencedistribution of beam 2314. Thus, the beam delivered to process head 2324will be a twice adjusted beam 2328 having a different beam divergenceprofile from that of adjusted beam 2314.

Process fibers 2304, 2320, and/or 2322 may comprise a RIP similar to anyof the second lengths of fiber described above, including confinementregions or a wide variety of other RIPs, and claimed subject matter isnot limited in this regard.

In yet another example, free-space optics switch 2332 may directadjusted beam 2314 to free-space optics assembly 2308 configured tochange the beam characteristics of adjusted beam 2314. Process fiber2322 may have a different RIP from that of VBC delivery fiber 2340 andmay be configured to preserve (or alternatively further modify) the newfurther adjusted characteristics of beam 2314. Thus, the beam deliveredto process head 2326 will be a twice adjusted beam 2330 having differentbeam characteristics (due to the adjusted divergence profile and/orintensity profile) from those of adjusted beam 2314.

In FIGS. 22A, 22B, and 23, the optics in the FFC or FFS may adjust thespatial profile and/or divergence profile by magnifying or demagnifyingthe beam 2214 before launching into the process fiber. They may alsoadjust the spatial profile and/or divergence profile via other opticaltransformations. They may also adjust the launch position into theprocess fiber. These methods may be used alone or in combination.

FIGS. 22A, 22B, and 23 merely provide examples of combinations ofadjustments to beam characteristics using free-space optics and variouscombinations of fiber RIPs to preserve or modify adjusted beams 2214 and2314. The examples provided above are not exhaustive and are meant forillustrative purposes only. Thus, claimed subject matter is not limitedin this regard.

FIG. 24 illustrates various examples of perturbation devices, assembliesor methods (for simplicity referred to collectively herein as“perturbation device 110”) for perturbing a VBC fiber 200 and/or anoptical beam propagating in VBC fiber 200 according to various examplesprovided herein. Perturbation device 110 may be any of a variety ofdevices, methods, and/or assemblies configured to enable adjustment ofbeam characteristics of a beam propagating in VBC fiber 200 in responseto application of one or more of various states of perturbation. Someexamples of various states of perturbation that may be applied to VBCfiber 200 include, but are not limited to, amount or direction ofbending, lateral mechanical stress, acoustic wave oscillation-inducedmechanical pressure, temperature variation, piezo-electric transducerdisplacement, and varying periodicity or amplitude of refractivegrating. A variation in one or more states establishes a different stateof perturbation. To vary one or more of these states, perturbationdevice 110 may be a mandrel 2402, a micro-bend 2404 in the VBC fiber,flexible tubing 2406, an acousto-optic transducer 2408, a thermal device2410, a piezo-electric device 2412, a grating 2414, a clamp 2416 (orother fastener), or the like, or any combination thereof. These aremerely examples of perturbation devices 100 and not an exhaustivelisting of perturbation devices 100, and claimed subject matter is notlimited in this regard.

Mandrel 2402 may be used to perturb VBC fiber 200 by providing a formabout which VBC fiber 200 may be bent. As discussed above, reducing thebend radius of VBC fiber 200 moves the intensity distribution of thebeam radially outward. In some examples, mandrel 2402 may be stepped orconically shaped to provide discrete bend radii levels. Alternatively,mandrel 2402 may comprise a cone shape without steps to providecontinuous bend radii for more granular control of the bend radius. Theradius of curvature of mandrel 2402 may be constant (e.g., a cylindricalform) or non-constant (e.g., an oval-shaped form). Similarly, flexibletubing 2406, clamps 2416 (or other varieties of fasteners), or rollers250 may be used to guide and control the bending of VBC fiber 200 aboutmandrel 2402. Furthermore, changing the length over which the fiber isbent at a particular bend radius also may modify the intensitydistribution of the beam. VBC fiber 200 and mandrel 2402 may beconfigured to change the intensity distribution within the first fiberpredictably (e.g., in proportion to the length over which the fiber isbent and/or the bend radius). Rollers 250 may move up and down along atrack 2442 on a platform 2434 to change the bend radius of VBC fiber200.

Clamps 2416 (or other fasteners) may be used to guide and control thebending of VBC fiber 200 with or without a mandrel 2402. Clamps 2416 maymove up and down along a track 2442 or a platform 2446. Clamps 2416 mayalso swivel to change bend radius, tension, or direction of VBC fiber200. A controller 2448 may control the movement of clamps 2416.

In another example, perturbation device 110 may be flexible tubing 2406and may guide bending of VBC fiber 200 with or without a mandrel 2402.Flexible tubing 2406 may encase VBC fiber 200. Tubing 2406 may be madeof a variety of materials and may be manipulated using piezoelectrictransducers controlled by a controller 2444. In another example, clampsor other fasteners may be used to move flexible tubing 2406.

Micro-bend 2404 in VBC fiber is a local perturbation caused by lateralmechanical stress on the fiber. Micro-bending can cause mode couplingand/or transitions from one confinement region to another confinementregion within a fiber, resulting in varied beam characteristics of thebeam propagating in a VBC fiber 200. Mechanical stress may be applied byan actuator 2436 that is controlled by controller 2440. However, this ismerely an example of a method for inducing mechanical stress in fiber200 and claimed subject matter is not limited in this regard.

Acousto-optic transducer (AOT) 2408 may be used to induce perturbationof a beam propagating in the VBC fiber using an acoustic wave. Theperturbation is caused by the modification of the refractive index ofthe fiber by the oscillating mechanical pressure of an acoustic wave.The period and strength of the acoustic wave are related to the acousticwave frequency and amplitude, allowing dynamic control of the acousticperturbation. Thus, a perturbation assembly 110 including AOT 2408 maybe configured to vary the beam characteristics of a beam propagating inthe fiber. In an example, a piezo-electric transducer 2418 may createthe acoustic wave and may be controlled by a controller or driver 2420.The acoustic wave induced in AOT 2408 may be modulated to change and/orcontrol the beam characteristics of the optical beam in VBC 200 inreal-time. However, this is merely an example of a method for creatingand controlling an AOT 2408, and claimed subject matter is not limitedin this regard.

Thermal device 2410 may be used to induce perturbation of a beampropagating in VBC fiber using heat. The perturbation is caused by themodification of the RIP of the fiber induced by heat. Perturbation maybe dynamically controlled by controlling an amount of heat transferredto the fiber and the length over which the heat is applied. Thus, aperturbation assembly 110 including thermal device 2410 may beconfigured to vary a range of beam characteristics. Thermal device 2410may be controlled by a controller 2450.

Piezo-electric transducer 2412 may be used to induce perturbation of abeam propagating in a VBC fiber using piezoelectric action. Theperturbation is caused by the modification of the RIP of the fiberinduced by a piezoelectric material attached to the fiber. Thepiezoelectric material in the form of a jacket around the bare fiber mayapply tension or compression to the fiber, modifying its refractiveindex via the resulting changes in density. Perturbation may bedynamically controlled by controlling a voltage to the piezo-electricdevice 2412. Thus, a perturbation assembly 110 including piezo-electrictransducer 2412 may be configured to vary the beam characteristics overa particular range.

In an example, piezo-electric transducer 2412 may be configured todisplace VBC fiber 200 in a variety of directions (e.g., axially,radially, and/or laterally) depending on a variety of factors, includinghow the piezo-electric transducer 2412 is attached to VBC fiber 200, thedirection of the polarization of the piezo-electric materials, theapplied voltage, etc. Additionally, bending of VBC fiber 200 is possibleusing the piezo-electric transducer 2412. For example, driving a lengthof piezo-electric material having multiple segments comprising opposingelectrodes can cause a piezoelectric transducer 2412 to bend in alateral direction. Voltage applied to piezoelectric transducer 2412 byan electrode 2424 may be controlled by a controller 2422 to controldisplacement of VBC fiber 200. Displacement may be modulated to changeand/or control the beam characteristics of the optical beam in VBC 200in real-time. However, this is merely an example of a method ofcontrolling displacement of a VBC fiber 200 using a piezo-electrictransducer 2412 and claimed subject matter is not limited in thisregard.

Gratings 2414 may be used to induce perturbation of a beam propagatingin a VBC fiber 200. A grating 2414 can be written into a fiber byinscribing a periodic variation of the refractive index into the core.Gratings 2414 such as fiber Bragg gratings can operate as opticalfilters or as reflectors. A long-period grating can induce transitionsamong co-propagating fiber modes. The radiance, intensity profile,and/or divergence profile of a beam comprised of one or more modes canthus be adjusted using a long-period grating to couple one or more ofthe original modes to one or more different modes having differentradiance and/or divergence profiles. Adjustment is achieved by varyingthe periodicity or amplitude of the refractive index grating. Methodssuch as varying the temperature, bend radius, and/or length (e.g.,stretching) of the fiber Bragg grating can be used for such adjustment.VBC fiber 200 having gratings 2414 may be coupled to a stage 2426. Stage2426 may be configured to execute any of a variety of functions and maybe controlled by a controller 2428. For example, stage 2426 may becoupled to VBC fiber 200 with fasteners 2430 and may be configured tostretch and/or bend VBC fiber 200 using fasteners 2430 for leverage.Stage 2426 may have an embedded thermal device and may change thetemperature of VBC fiber 200.

FIG. 25 illustrates an example process 2500 for adjusting and/ormaintaining beam characteristics within a fiber without the use offree-space optics to adjust the beam characteristics. In block 2502, afirst length of fiber and/or an optical beam are perturbed to adjust oneor more optical beam characteristics. Process 2500 moves to block 2504,where the optical beam is launched into a second length of fiber.Process 2500 moves to block 2506, where the optical beam having theadjusted beam characteristics is propagated in the second length offiber. Process 2500 moves to block 2508, where at least a portion of theone or more beam characteristics of the optical beam are maintainedwithin one or more confinement regions of the second length of fiber.The first and second lengths of fiber may be comprised of the samefiber, or they may be different fibers.

Non-circular confinement regions or non-coaxial confinement regions inthe second length of fiber of a VBC fiber enable production of laseroutput beams exhibiting intensity distribution profiles having non-zeroellipticity in multiple orientations. In one application, ellipticalbeams can advantageously be used to locally control microstructures ofadditively deposited materials to directly engineer site-specificproperties. One example is reprocessing regions deposited by circularlaser beam intensity profiles to reduce surface roughness. An ellipticalbeam can be formed in multiple elliptical shapes and orientations by aVBC fiber without use of downstream bulk optics and the consequentdisadvantages of cost, complexity, size, weight, optical loss,misalignment, and sensitivity to contamination and environmentalconditions.

The several embodiments of VBC fibers described below are constructed inaccordance with the disclosed paradigm represented by example VBC fiber100 illustrated in FIG. 1. An optical beam 102 emitted by an externalsource (not shown) and incident on VBC fiber 100 is processed inresponse to operation of a perturbation device 110 to produce an outputthat exhibits an intensity distribution profile having non-zeroellipticity generated by the configurations of the respective first andsecond lengths of fiber 104 and 108 of these several embodiments.

FIG. 29A illustrates a VBC fiber 2900 representing a first optical fiberembodiment, which includes first and second lengths of fiber that areconfigured and coupled together to produce an output exhibiting anannular elliptical intensity profile. VBC fiber 2900 includes a secondlength of fiber 2908 of similar construction to that of second length offiber 208 of FIG. 2, with the exception of the former having concentricelliptical confinement regions. FIG. 29B illustrates a cross-sectionalview of second length of fiber 2908, showing the concentric ellipticalconfinement regions.

VBC fiber 2900 comprises a first length of fiber 2904 and second lengthof fiber 2908 that are coupled together at a splice junction 2906 anddefine a longitudinal axis 2907. First length of fiber 2904 has aparabolic graded-index (GRIN) RIP 2912 in a radially central region, asindicated by the left RIP graph of FIG. 29A. Most of the intensitydistribution of an optical beam 2902 propagating in first length offiber 2904 is concentrated in the center of first length of fiber 2904when it is straight or nearly straight. Second length of fiber 2908 is aconfinement fiber having RIPs 2930 and 2932 at two azimuthal angles asshown in FIG. 29B. Second length of fiber 2908 includes confinementregions 2916, 2918, and 2920. Confinement region 2916 is a central coreor confinement region surrounded by two annular elliptical confinementregions 2918 and 2920. (The term “confinement region” is conventionallyreferred to as a “core” in a standard fiber, and these two terms areused interchangeably throughout the descriptions presented.) Althoughthey are aligned in FIG. 29B, the major axes of elliptical confinementregions 2918 and 2920 in the general case are not aligned. Layers 2922and 2924 are structural barriers of lower index material betweenconfinement or cladding regions (2916, 2918, and 2920). In one example,barrier layers 2922 and 2924 may comprise rings of fluorosilicate; insome embodiments, the fluorosilicate cladding layers are relativelythin. Other material may be used as well, and claimed subject matter isnot limited in this regard.

In an example, as optical beam 2902 propagates along VBC fiber 2900, aperturbation assembly 2910 bends fiber 2904 to adjust the beamcharacteristics of optical beam 2902 and generate an adjusted opticalbeam 2926. In the current example, the intensity distribution of beam2902 is modified by perturbation assembly 2910. In the current example,perturbation assembly 2910 is implemented with a stepped mandrel, asillustrated in FIG. 3. Perturbation assembly 2910 may also beimplemented with any one of the other examples of VBC perturbationdevice 110 illustrated in FIG. 24. Perturbation assembly 2910 shifts theradial position of optical beam 2902 to form adjusted optical beam 2926.Subsequent to adjustment of optical beam 2902, the intensitydistribution of adjusted optical beam 2926 may be concentrated in outerconfinement regions 2918 and 2920 with relatively little intensity incentral confinement region 2916. Because confinement regions 2916 and2918 and confinement regions 2918 and 2920 are isolated by the thinlayers of lower index material in barrier layers 2924 and 2922,respectively, second length of fiber 2908 can substantially maintain theadjusted intensity distribution of adjusted optical beam 2926. Adjustedoptical beam 2926 will typically become distributed azimuthally within agiven confinement region but will not significantly transition betweenthe confinement regions as it propagates along second length of fiber2908. Thus, the adjusted beam characteristics of adjusted optical beam2926 are largely conserved within any one or a combination of theisolated confinement regions 2916, 2918, and 2920. In some cases, it maybe desirable to have the power of adjusted optical beam 2926 dividedamong confinement regions 2916, 2918, and 2920 rather than concentratedin a single region, and this condition may be achieved by generating anappropriately adjusted beam 2926.

FIG. 29C is a diagram showing examples of annular elliptical intensitydistribution profiles formed by confinement regions 2918 and 2920 andproduced at the output of second length of fiber 2908. An annularintensity distribution profile pattern P2918 formed by annularconfinement region 2918 has an inner border that is contiguous with thesurface of circular confinement region 2916, has an outer border that iscontiguous with the inner border of confinement region 2920, and ispositioned closer to central longitudinal axis 2907. An annularintensity distribution profile pattern P2920 formed by annularconfinement region 2920 has an inner border that is contiguous with theouter border of annular confinement region 2918 and is positioned fromfarther from longitudinal axis 2907.

FIG. 30A illustrates VBC fiber 3000 representing a second optical fiberembodiment, which includes first and second lengths of fiber that areconfigured and coupled together to produce an output exhibiting anelliptical intensity profile in different orientations. VBC fiber 3000includes a second length of fiber 3008 having multiple offset,non-coaxial elliptical confinement regions. FIG. 30B illustrates across-sectional view of second length of fiber 3008, showing the offset,non-coaxial elliptical confinement regions.

VBC fiber 3000 comprises a first length of fiber 3004 and second lengthof fiber 3008 that are coupled together at a splice junction 3006 anddefine a longitudinal axis 3007. First length of fiber 3004 has aparabolic graded-index RIP 3012 in a radially central region, asindicated by the left RIP graph of FIG. 30A. Second length of fiber 3008includes a first elliptical confinement region 3016 having a first majoraxis 3016 a and second elliptical confinement region 3018 having asecond major axis 3018 a. Second length of fiber 3008 is an azimuthallyasymmetric multi-core fiber because first and second ellipticalconfinement regions 3016 and 3018 are non-coaxial and are spatiallyoffset from each other. First and second major axes 3016 a and 3018 aare illustrated as orthogonally aligned with each other, but they may bealigned at an arbitrary angle relative to each other. First and secondmajor axes 3016 a and 3018 a have, respectively, center points 3016 cand 3018 c, which are collinear with longitudinal axis 3007, asillustrated in FIG. 30B.

A perturbation assembly 3010 perturbs VBC fiber 3000 by an amount thatshifts the radial position of an optical beam 3002 propagating throughfirst length of fiber 3004 to form an adjusted optical beam 3026.Adjusted optical beam 3026 launches into one of first and secondelliptical confinement regions 3016 and 3018, depending on the amount ofperturbation that is imparted to VBC fiber 3000 in response to forceapplied by perturbation device 3010. In some implementations, theperturbation includes bending of VBC fiber 3000. To launch adjustedoptical beam 3026 into the different regions occupied by ellipticalconfinement regions 3016 and 3018 of azimuthally asymmetric secondlength of fiber 3008, perturbation assembly 3010 acts in multipleplanes, as stated with reference to FIG. 27 and described in morespecific detail below.

An example of perturbation assembly 3010 is a VBC perturbative device110, which is shown in FIG. 24, applying micro-bend 2404 to VBC fiber200. VBC perturbative device 110 can be configured to control in oneaxis or two axes the direction of the beam propagating in VBC fiber 200.This is accomplished by imparting micro-bend 2404 to VBC fiber 200.Micro-bend 2404 in VBC fiber 200 is a local perturbation caused bylateral mechanical stress applied to the fiber. Micro-bending can causeone or both of mode coupling and transitions from one confinement regionto another confinement region within a fiber, resulting in varied beamcharacteristics of the beam propagating in VBC fiber 200. Mechanicalstress may be applied by an actuator 2436 that is controlled by acontroller 2440. Actuator 2436 includes two actuator probes 2436 a and2436 b positioned to apply mechanical stress to VBC fiber 200 inorthogonal directions and thereby direct the beam propagating in VBCfiber 200 to any location in a two-dimensional space. Although it ispresented with reference to VBC fiber 200, the foregoing description ofthe operation of VBC perturbative device 110 applies also to VBC fiber3000. However, this is merely an example of a method of inducingmechanical stress in VBC fiber 3000, and the claimed subject matter isnot limited in this regard. Perturbation assembly 3010 may also beimplemented with any one of the other examples of VBC perturbationdevice 110 illustrated in FIG. 24.

The one of first and second elliptical confinement regions 3010 and 3018receiving adjusted optical beam 3026 delivers an output exhibiting anelliptical intensity distribution profile in an orientation establishedin relation to the azimuthal position of the major axis of theelliptical confinement region that received adjusted optical beam 3026.FIG. 30B illustrates RIPs 3030 and 3032 at two azimuthal angles of across-section of second length of multi-core fiber 3008.

FIG. 30C is a diagram showing examples of elliptical intensitydistribution profiles P3016 and P3018 separately formed by confinementregions 3016 and 3018, respectively, and produced during different timesat the output of second length of fiber 3008.

FIG. 31A illustrates a VBC fiber 3100 representing a third optical fiberembodiment, which includes first and second lengths of fiber that areconfigured and coupled together to produce an output exhibitingintensity distribution profiles having, on average, non-zeroellipticity. VBC fiber 3100 includes a second length of fiber 3108 ofsimilar construction to that of multi-core fiber 2700, with multipleclosely spaced-apart circular cores. FIG. 31B illustrates across-sectional view of second length of fiber 3108.

VBC fiber 3100 comprises a first length of fiber 3104 and second lengthof multi-core fiber 3108 that are coupled together at a splice junction3106, and define a longitudinal axis 3107. First length of fiber 3104has a parabolic graded-index RIP 3112 in a radially central region, asindicated by the left RIP graph of FIG. 31A. Second length of multi-corefiber 3108 includes mutually closely spaced-apart circular confinementregions 3116, 3118, and 3120. Confinement region 3116 is a central corehaving a center 3116 c that coincides with longitudinal axis 3107.Confinement region 3118 having a center 3118 c and confinement region3120 having a center 3120 c are non-coaxial cores. Center 3118 c ofconfinement region 3118 is positioned along the X-axis, and center 3120c of confinement region 3120 is positioned along the Y-axis. Confinementregions 3116, 3118, and 3120 are mutually closely spaced-apart from eachother with edge-to-edge spacing of the confinement regions between about5 times and about 20 times the wavelength of light propagating in theconfinement regions to form an output intensity distribution profilehaving non-zero ellipticity in the manner described below.

An example of a perturbation assembly 3110 is VBC perturbative device110 applying micro-bend 2404 as shown in FIG. 24. Actuator probes 2436 aand 2436 b of actuator 2436 can be positioned to apply, either atdifferent times or at the same time, mechanical stress to VBC fiber 3100and thereby direct optical beam 3102 propagating in VBC fiber 3100 tolocations along the X-axis and Y-axis, respectively. Controller 2440providing a signal that causes probe 2436 a to impart a micro-bend 2404x to VBC fiber 3100 may move optical beam 3102 along the X-axis to shiftthe energy distribution of adjusted optical beam 3126 outward toconfinement regions 3016 and 3018. Similarly, controller 2440 providinga signal that causes probe 2436 b to impart a micro-bend 2404 y to VBCfiber 3100 may move optical beam 3102 along the Y-axis to shift theenergy distribution of adjusted optical beam 3126 outward to confinementregions 3116 and 3120. Controller 2440 providing signals that causeprobes 2436 a and 2436 b to concurrently impart the respectivemicro-bends 2404 x and 2404 y to VBC fiber 3100 may move beam 3102 tolocations in an X-Y plane to shift the energy distribution of adjustedoptical beam 3126 outward to non-coaxial confinement regions 3118 and3120.

In all three instances, some of the energy intensity is present in oneof the pairs of confinement regions 3116, 3118, and 3120. The excitationof each confinement region of a pair of cooperatively orientedconfinement regions results in the synthesis of an output intensitydistribution profile having non-zero ellipticity. FIG. 31B illustratesRIPs 3130 and 3132 at two azimuthal angles of a cross-section of secondlength of multi-core fiber 3108.

Controller 2440 providing signals that cause probes 2436 a and 2436 b toimpart the respective micro-bends 2404 x and 2404 y to VBC fiber 3100may, in the alternative, dither adjusted optical beam 3126 betweenconfinement regions of any one of the pairs of confinement regions 3116,3118, and 3120. Sufficiently high frequency dithering of excitation ofeach confinement region of a pair of confinement regions results in anoutput intensity distribution profile having, on average, non-zeroellipticity. Perturbation assembly 3110 may also be implemented formoving optical beam 3102 to locations in an X-Y plane by any one of theother examples of VBC perturbation device 110 illustrated in FIG. 24.

FIG. 31C is a diagram showing examples of output intensity distributionprofiles having non-zero ellipticity generated for each pair ofconfinement regions 3116, 3118, and 3120. Intensity distribution profilepatterns P16-18, P16-20, and P18-20, represent those formed byconfinement region pairs 3116 and 3118, 3116 and 3120, and 3118 and3120, respectively, when observed at a distance from the output end ofsecond length of multi-core fiber 3108. The extent of apparent overlapof the light emitted by any one of the pairs of circular confinementregions depends on the separation between them, their radii, anddivergence of the output beam. When observed at the output end of secondlength of multi-core fiber 3108, each of intensity distribution profilepatterns P16-18, P16-20, and P18-20 would appear as two separatecircular confinement regions with no output light connecting them. FIG.31C illustrates that the long dimension of the intensity distributionprofile pattern synthesized by each pair of circular confinement regionsis established by a line connecting their centers.

Having described and illustrated the general and specific principles ofexamples of the presently disclosed technology, it should be apparentthat the examples may be modified in arrangement and detail withoutdeparting from such principles. We claim all modifications and variationcoming within the spirit and scope of the following claims.

1. An optical beam delivery device formed of optical fibers configuredto produce an output exhibiting an intensity distribution profile havingnon-zero ellipticity, comprising: a first length of fiber through whichan incident optical beam having beam characteristics propagates andwhich has a first refractive index profile (RIP), the first RIPenabling, in response to an applied perturbation, modification of thebeam characteristics of the optical beam to form an adjusted beam havingmodified beam characteristics relative to the beam characteristics ofthe optical beam; and a second length of fiber coupled to the firstlength of fiber and formed with a set of one or more confinement regionsdefining a second RIP and arranged to confine at least a portion of theadjusted beam to generate, at an output of the second length of fiber,an intensity distribution profile having non-zero ellipticity.
 2. Theoptical beam delivery device of claim 1, in which the set of one or moreconfinement regions includes non-coaxial first and second ellipticalconfinement regions defining respective first and second major axes, thefirst and second elliptical confinement regions being spatially offsetfrom each other, and the first and second major axes being aligned at anarbitrary angle with each other.
 3. The optical beam delivery device ofclaim 2, in which the first and second major axes are orthogonallyaligned relative to each other.
 4. The optical beam delivery device ofclaim 1, in which the set of one or more confinement regions includes aplurality of non-coaxial circular confinement regions, and in whichdifferent pairs of closely spaced ones of the plurality of non-coaxialcircular confinement regions are oriented cooperatively to generate, atthe output of the second length of fiber, the intensity distributionprofile having non-zero ellipticity.
 5. The optical beam delivery deviceof claim 4, in which the modified beam characteristics include radialposition of the adjusted beam, and in which the applied perturbationdithers the radial position of the adjusted beam between confinementregions forming one of the different pairs of closely spaced ones of theplurality of non-coaxial circular confinement regions to synthesize theintensity distribution profile having, on average, non-zero ellipticity.6. The optical beam delivery device of claim 1, in which the set of oneor more confinement regions includes a central confinement region and anelliptical confinement region that is coaxial with the centralconfinement region.
 7. The optical beam delivery device of claim 1, inwhich set of one or more confinement regions includes a centralconfinement region and first and second elliptical confinement regionsthat are coaxial with the central confinement region, the firstelliptical confinement region having an outer boundary, and the secondelliptical confinement region having an inner boundary that iscontiguous with the outer boundary of the first elliptical confinementregion.
 8. The optical beam delivery device of claim 1, in which thefirst RIP comprises a graded index RIP in a radially central portion ofthe first length of fiber.
 9. The optical beam delivery device of claim1, in which the applied perturbation bends the first length of fiber toposition the adjusted beam to a location in a two-dimensional plane. 10.The optical beam delivery device of claim 1, further comprising aperturbation device to produce the applied perturbation.
 11. The opticalbeam delivery device of claim 10, in which the perturbation deviceincludes an actuator and a controller to control in two or more axes aselected state of different states of the applied perturbation.
 12. Theoptical beam delivery device of claim 11, in which the different statesof the applied perturbation are different radii of bend of the opticalbeam delivery device.
 13. The optical beam delivery device of claim 11,in which the different states of the applied perturbation are differentdirections of bend of the optical beam delivery device.